The process of the present invention relates to the removal of impurity components from sulphidic and metallized molten copper mattes obtained in the pyrometallurgical processing of sulphidic complex and mixed copper ores, which said mattes often contain very large amounts of impurities. The very great difficulties associated with these impurity metals Pb, Zn, Ni, Co, As, Sb, Bi, Se, Te etc., in pyrometallurgical methods of copper refining are generally known. These impurities do not pass into the slag or volatilize to a sufficient extent in the processing of ores to crude metal. In pyrometallurigcal processes compounds of these metals or metalloids, which dissociate easily to the metal, follow the principal metal throughout the processing. At every stage of the processing an effort is made to remove these impurity compounds because if they remain in the crude metal they render it more difficult to refine and their presence even in very low concentrations in the final product is detrimental.
In the production of copper by means of customary methods (matte smelting, conversion) removal of part of the arsenic, antimony, bismuth, lead etc. present in concentrates and ores is achieved, but nevertheless not to a sufficient extent. In connection with the production of sulphide mattes it is possible to influence the elimination of the impurities being considered by choice of a suitable smelting technique. When using shaft, reverberatory and electric furnaces about half the mentioned impurities remain in the sulphide phase. Results considerably better than this, particularly in respect of arsenic and bismuth, are obtained in suspension smelting processes especially when smelting sulphide mattes rich in value metals.
Irrespective of the method of smelting used and even for ores or concentrates having relatively low contents of Pb(Co,Ni) and As(Sb,Sn) it may happen that the resulting melt divides into two layers. This is because of the formation of an arsenide-antimonide melt in addition to the sulphide melt. This arsenide-antimonide melt is metallurigically an extremely undesirable intermediate product containing so-called speiss forming metals, i.e. Co, Ni, Fe, As, Sb, Au, Ag, Te, Cu, Sn, Pb, Se. If the melt contains a considerable amount of lead then a crude lead phase will also be formed in addition to sulphide and arsenide phases.
Known processes comparable in their technical standard to novel inventions include fairly numerous sub-processes and combinations of processes relating to the treatment of arsenide-antimonide mattes.
The recovery of the components of arsenide-antimonide mattes only started early in this century. A view of the standard and changes in process technology during this century can be gained from the following publications among others: C. Guillemain: Metallurgie, VII, 1910, 595-602; H. Kleinheisterkamp: Erzmetall, I, 1948, 247-253; L. Fontainas, M. Coussement, R. Maes: Trans Instn Min Met, 88, 1979, 13-23.
The arsenide-antimonide matte separated in preliminary smelting or conversion is usually metallized, i.e. it generally contains large amounts of copper and lead in so-called physical solution and is lean in respect of actual speiss-forming metals. The first stage in refining the matte is its enrichment in respect of arsenic, antimony, nickel and cobalt.
Lead concentrate can be used for enrichment of the matte, particularly if the matte has a high lead content to start with. If this is done, part of the iron and copper present in the arsenide matte pass into the sulphide phase. Lead separates out into a phase of its own, in which antimony freed by decomposition of antimonides dissolves EQU Fe(2Cu)+PbS.rarw..fwdarw.FeS(Cu.sub.2 S)+Pb EQU 2Cu.sub.3 Sb+3PbS.rarw..fwdarw.3Ci.sub.2 S+3Pb+2Sb
The direct use of elemental sulphur in the enrichment of arsenide matte has been proposed, Blanderer: Erzmetall, XVII, 1964, 247-253. After enrichment the melt can be further sulphidated with elemental sulphur, thereby displacing arsenic from the arsenides. This is not generally done in practice, however, because as a consequence of the low partial pressure of arsenic large excesses of sulphur are required.
The successful processing of arsenide-antimonide matte is associated with the problem of separating the arsenic and antimony as completely as possible from the other components of the matte. For these other components (Co, Ni, Cu, Pb, Sn, Ag, Au) excellent hydrometallurgical separation processes have been developed. Some methods which have been developed for the separation of arsenic and antimony from similar mattes will be examined. The good volatility of arsenic and its compounds has long been known.
The distillation of arsenic, exploiting the dissociation of arsenides, does not yield quantitative results. The volatilization of arsenic for example from nickel and cobalt attains a value of 10% only at temperatures above 1000.degree. C.
The decomposition and sulphide volatilization of arsenides using elemental sulphur has already been dealt with. The decomposition of solid arsenides and the sulphidic volatilization of arsenic has been successfully tried also using iron pyrites as the source of sulphur, H. W. Loose: Chemismus der Entfernung von Arsen aus seinen Verbindungen mit Eisen, Kupfer, Nickel und Kobalt durch Erhitzen in Anwesenheit von Pyrit, Berlin 1931, 1-63. The addition of iron sulphide, however, reduces the concentration of sulphides of value metals in the product to such an extent that the process is not considered economic. The arsenic volatilization process according to U.S. Pat. No. 1,718,825 is also based on the use of sulphur, the arsenides being mixed with substances containing sulphur and with coal in sufficient quantity to form a self-roasting mixture. While roasting the mixture in this process a low-oxygen COS atmosphere is maintained.
Chlorination of the arsenic in arsenide mattes is effective, but technical problems have prevented the use of such processes. When the matte is chlorinated at a temperature below 600.degree. C. both arsenic and iron volatilize as chlorides, U.S. Pat. No. 1,406,595. When arsenide matte is roasted at a temperature of approx. 800.degree. C. in the presence of hydrochloric acid the arsenic is volatilized completely.
Customary methods of treating arsenides include the oxidizing calcination of arsenic (and antimony). The methods do not, however, lead to the quantitative elimination of arsenic. At temperatures over 300.degree. C. the volatile arsenic trioxide formed in the oxidation has a tendency to disproportion and the nascent pentoxide unites with metal oxides to form arsenates. Written for cobalt the reaction is EQU 2Co.sub.5 As.sub.2 +9O.sub.2 .rarw..fwdarw.5CoO.As.sub.2 O.sub.5 +5CoO+As.sub.2 O.sub.3
Many methods have been proposed to prevent the formation of arsenates. A good method is calcination in the presence of sulphur dioxide, as a result of which arsenates decompose and arsenic pentoxide is reduced. In respect of cobalt even this method of calcination is inadequate, because at a temperature of 1100.degree. C. the volatilization of arsenic only corresponds to a value of 70%. Because complete oxidative volatilization is not feasible, it is often desired that the arsenic content of the product is high enough to permit precipitation of iron arsenate in hydrometallurgical refining.
Mention may also be made of the industrially used method of soda calcination of arsenide matte based on U.S. Pat. No. 1,505,718 and DE Pat. No. 1 129 707, in which arsenic is converted to water-soluble sodium arsenate. Another important method is the direct autoclave leaching of arsenide matte in accordance with DE Pat. No. 545 836, in which the arsenic and antimony acids obtained as a product are hydrolyzed to oxides with the value metals remaining in solution as sulphates.
It is an object of the present invention to provide a combination of methods which is more advantageous than previous methods in the processing of molten phases, principally of copper, containing harmful impurities.